Hitherto, an introduction of reactive silyl groups into acrylic resins has been attempted from the viewpoints that silicone resins have an excellent weatherability, heat resistance and chemical resistance and that acrylic resins have an excellent weatherability and heat resistance.
The present inventors have already succeeded in preparation of telechelic vinyl resins where alkoxysilyl groups are introduced at both terminals, by subjecting disulfide compounds having a specific alkoxysilyl group and various vinyl monomers including an acrylic monomer to photopolymerization reaction, which is a pending patent application (see Japanese Patent Application No. 211667/1985 =U.S. Ser. No. 086241 now abandoned and EP-A-0217178). However, in case that the vinyl resins have too high number average molecular weight, resin viscosity or solution viscosity of the resins becomes extremely high, resulting in a decreased workability when used. Further it has problems during the preparation, i.e. when the disulfide compounds and the acrylic monomers are subjected to photopolymerization reaction, owing to exothermic reaction by rapid polymerization, the temperature inside the vessel is remarkably raised, which induces an extreme increase in a viscosity or gelation of the produced polymer. In addition, when the reaction is conducted on a large scale, the inner pressure of the reaction vessel increases by the exothermic reaction, which creates a too dangerous condition to continue the reaction.
Under such circumstances, the present inventors have studies intensively to solve the above-mentioned problems. As a result, the present inventors have found that vinyl resins of a low molecular weight having a good workability when used can be prepared by employing a specific tetrasulfide compound in addition to the disulfide compound in the above photopolymerization reaction and by specifying a ratio of the reaction components and that the photopolymerization reaction can be carried out safely even on a large amount scale by controlling the generation of heat through decrease of a polymerization rate. Thus the present invention has now been completed.